Use of electronic portal imaging to assess cardiac irradiation in breast radiotherapy.

An audit was performed to assess the frequency of cardiac irradiation in patients receiving radiotherapy for left-sided breast cancer. Images from an 'online' electronic portal imaging device were reviewed in patients who were treated with a tangential pair of megavoltage fields. In 169 consecutive patients treated on a Philips SL25 6 MV linear accelerator equipped with an SRI 100 imaging device, the cardiac apex was included in the radiotherapy field in 15 patients (9%). The long term sequelae of such cardiac irradiation is uncertain. The results of this audit suggest that careful treatment technique and quality control with portal imaging can minimize unnecessary cardiac irradiation in the majority of patients.